A typical power delivery system in a workstation or PC includes a power source or supply, such as a battery or a 120 v or 240 v AC supply and an AC/DC converter, converts the voltage from the source to a supply suitable for electronic components (e.g., 1.6 v, 5 v DC or any other voltage), and delivers the voltage to the components. In computing devices such as PCs and workstations, the central processing unit (“CPU,” also termed microprocessor) typically has strict voltage tolerance requirements. The CPU alternately draws power or is idle, switching between full power consumption and no power consumption extremely quickly. The power delivery system should respond to the power demands of the CPU while providing a voltage that always remains within certain tolerances.
A power delivery system typically includes a voltage source followed by several stages of decoupling capacitors. When used herein, a decoupling stage (or “stage”) is a division of a power delivery system, such as circuit including a set of capacitors and possibly other components or equipment. A decoupling stage may include parasitic inherent resistive and inductive elements. The power source (often termed Vreg or Vemf) is typically a DC supply supplying a certain voltage or set of voltages from the processed output of the ultimate power source—typically a battery or the processed output of an AC supply. The power source usually cannot respond quickly to fast current demand changes; in response to such changes the voltage supplied may fluctuate greatly.
The power delivery system is divided at several stages between the Vreg and the CPU itself, typically with arrangements of sets of capacitors of various values, in order to ensure that the voltage delivered to the CPU is within the required tolerance window despite rapid current demand fluctuations. Each set of capacitors is characterized by capacitance and associated parasitic inherent and interconnect resistance and inductance. Furthermore, each set of capacitors may include purposefully increased resistance; for example, additional resistive elements added to, added within, or connected to capacitors. For example, a typical power delivery system includes bulk (BLK) capacitors disposed on the motherboard and connected to the Vreg. While the bulk capacitors improve response time, they are typically physically large which leads to a considerable parasitic inductance, limiting the overall response time of these capacitors. Further sets of capacitors may be included on the motherboard (e.g., mid-frequency (MF) capacitors), in the package containing the CPU (PKG) and on silicon chip itself (DIE). At each stage (e.g., BLK, MF, PKG, DIE, etc.) the components improve response time through the damping effects of the capacitance. Multiple stages are usually needed. As the power delivery system progresses from the Vreg source to the die, the inductance of the capacitors typically decreases, as does the capacitance. The capacitance and the resistance of the capacitors at each stage may be adjusted to optimize the performance of that stage.
Thus, the typical power delivery system includes, inter alia, a power source Vreg and a series of stages leading up to the silicon chip itself. Current design methods, based essentially on trial and error, do not produce the ideal definition for the specifications for these components. Design inefficiencies in a power delivery system may result in too many or too few capacitors, or the incorrect type of capacitors, which may result in increased cost or the system not meeting the proper voltage tolerances.
One current method for reducing the cost of power supply systems while allowing the system to meet voltage tolerances provides for a voltage regulator where a smaller capacitance may be used while still allowing the regulator to provide voltage within the proper boundaries. According to this method, the voltage Vcc of the power source may be set to VccNom+Tolerance, where VccNom is the previous nominal value of Vcc, and Tolerance is the acceptable tolerance of the power delivery system. This adjustment allows a reduction in the capacitance of the stage immediately following the power source, typically the bulk capacitor stage. After the parameters of the power supply are set, the resistance of the bulk capacitors is set equal to the resistance of the voltage regulator. The capacitance of the bulk capacitors is then selected so that the time constant of the bulk capacitors is set equal to the time constant of the voltage regulator. Such a method does not optimize the design of an entire power delivery system.
Therefore, a need exists for power delivery systems that are both efficient and provide power within the stated tolerances, and for a method for designing such systems.